Fixed #8881 by specifying the geometry column name; added the `geom_col_name`...

Fixed #8881 by specifying the geometry column name; added the `geom_col_name` classmethod to `GeometryColumns` for Oracle and PostGIS.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8994 bcc190cf-cafb-0310-a4f2-bffc1f526a37